arcv: fuse load-immediate with dependent branch

With this commit, we allow a load-immediate to be macro-op fused with a
successive conditional branch that is dependent on it, e.g.:

li  t0, #imm
bge t1, t0, .label

Additionally, add a new testcase to check that this fusion type is
handled correctly.

Signed-off-by: Artemiy Volkov <artemiy@synopsys.com>

Author: artemiy-volkov

gcc/config/riscv/riscv-protos.h

@@ -822,6 +822,7 @@ extern unsigned int th_int_get_save_adjustment (void);
 extern rtx th_int_adjust_cfi_prologue (unsigned int);
 extern const char *th_asm_output_opcode (FILE *asm_out_file, const char *p);
 
+extern bool riscv_macro_fusion_p ();
 extern bool riscv_is_micro_arch (enum riscv_microarchitecture_type);
 
 #ifdef RTX_CODE

gcc/config/riscv/riscv.cc

@@ -10324,7 +10324,7 @@ riscv_sched_variable_issue (FILE *, int, rtx_insn *insn, int more)
 /* Implement TARGET_SCHED_MACRO_FUSION_P.  Return true if target supports
    instruction fusion of some sort.  */
 
-static bool
+bool
 riscv_macro_fusion_p (void)
 {
   return tune_param->fusible_ops != RISCV_FUSE_NOTHING;
@@ -10470,7 +10470,18 @@ arcv_macro_fusion_pair_p (rtx_insn *prev, rtx_insn *curr)
   /* prev and curr are simple SET insns i.e. no flag setting or branching.  */
   bool simple_sets_p = prev_set && curr_set && !any_condjump_p (curr);
 
-  /* Don't handle anything with a jump.  */
+ /* Fuse load-immediate with a dependent conditional branch.  */
+ if (get_attr_type (prev) == TYPE_MOVE
+     && get_attr_move_type (prev) == MOVE_TYPE_CONST
+     && any_condjump_p (curr))
+    {
+      rtx comp = XEXP (SET_SRC (curr_set), 0);
+
+      return (REG_P (XEXP (comp, 0)) && XEXP (comp, 0) == SET_DEST (prev_set))
+	  || (REG_P (XEXP (comp, 1)) && XEXP (comp, 1) == SET_DEST (prev_set));
+    }
+
+  /* Don't handle anything with a jump past this point.  */
   if (!simple_sets_p)
     return false;
 

gcc/testsuite/gcc.target/riscv/arcv-fusion-limm-condbr.c

@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mtune=arc-v-rhx-100-series" } */
+
+int
+f (int x)
+{
+  begin:
+  if (x <= 3)
+    goto begin;
+}
+
+/* { dg-final { scan-assembler "\\sli\\sa5,3\n\\sble\\sa0,a5,.L\[0-9\]+\n" } } */